As I understand it, this is something that would pop up occasionally when building a mining starbase in earlier versions. But I'm seeing a lot of planets being generated with the name "Thulium" in the new opt-in patch. In my first game, almost half of the stars I've explored have a Class 0 Dead Planet named Thulium. I started another game with different settings, removed fog of war, and looked around, saw a lot of Thulium planets.
In every single case, the name "Thulium" replaced what would have been planet number 1. i.e., I saw a system with 6 planets, Walleye, and the planets were Walleye II, III, IV, V, VI, and Thulium. No "Walleye I" but "Thulium." Some stars did generate with all planets correctly named, even when #1 was a class 0.
So far this has been nothing more than a minor curiosity, but I felt it should be noted.
EDIT: I just generated another new system, this time with resources set to None. No planets named Thulium were generated.